1. Field of the Invention
The present invention relates a time information obtaining device to receive a standard time radio wave so as to obtain time information thereof, and a radio clock mounted with the time information obtaining device.
2. Description of the Related Art
Presently, in countries such as Japan, Germany, the United Kingdom, Switzerland, and the like, a standard time radio wave having a long wave is transmitted from transmitting stations. For example, in Japan, standard time radio waves of 40 kHz and 60 kHz, which are performed with an amplitude modulation, are transmitted from a transmitting station located in Fukushima prefecture and in Saga prefecture, respectively. The standard time radio wave contains a sequence of codes which configure a time code indicating year/month/day/hour/minute, so that the time code is transmitted in 60 seconds per one period. That is to say, a period of the time code is 60 seconds.
There has been in practical use ad clock (a radio clock) in which the standard time radio wave including such time code is received, the time code is extracted from the received standard time radio wave, and the time can be corrected A reception circuit of the radio clock comprises a band-pass filter (BPF) to receive the standard time radio wave received by an antenna and to extract only a standard time radio wave signal; a demodulation circuit to demodulate the standard time radio wave signal which has been performed with an amplitude modulation by an envelope detection, and the like; and a processing circuit to read the Lime code included in the signal which is demodulated by the demodulation circuit.
In the conventional processing circuit, a synchronization is performed at the rising of the demodulated signal, a binarization is performed at a predetermined sampling period, and a TCO data having a unit of time length (1 second) which is a binary bit sequence is obtained. Further, the processing circuit measures the pulse width (that is to say, the time during a bit “1”, and a bit “0”) of the TCO data, determines either one of the codes of “P”, “0”, and “1” according to the size of the width, and obtains the time information based on the sequence of the determined code.
The conventional processing circuit undergoes the process of: second synchronization processing; minute synchronization processing; a code incorporation; and a matching judgment, from the starting of the reception of the standard time radio wave to the obtaining of the time information. When the processing cannot be terminated suitably in each process, the processing circuit is required to undergo the processing again from the beginning. Thus, there may be a case in which the processing has to be performed over and over again due to the influence of the noises included in the signal, which results in the time until the time information can be obtained being extremely long.
The second synchronization is to detect the rising of the code which happens every 1 second, among the codes indicated by the TCO data. By repeating the second synchronization, one can detect the portion where a position marker “P0” positioned at an ending of a frame, and a marker “M” positioned at a beginning of the frame are continued. The continued portion is to appear every 1 minute (60 seconds) The position of the marker “M” is where the data of the beginning frame exists among the TCO data. This detection is referred to as the minute synchronization.
Since the beginning of the frame is recognized by the above mentioned minute synchronization, the incorporation of the codes is thereafter started. After the data for 1 frame is obtained, a parity bit is checked, and whether it is an impossible value (a value in which the year/month/day/minute/second cannot be realized), or not is judged (the matching judgment). For example, since the minute synchronization is to detect the beginning of the frame, the minute synchronization may take 60 seconds. Of course, in order to detect the beginning of the plurality of frames, it may take several times longer.
In the disclosure of US2005/0195690A1, a demodulated signal is performed with a binarization at a predetermined sampling interval (50 ms) so as to obtain the TCO data. Further, a data group which comprises a binary bit sequence for every 1 second (20 samples) is listed. The device disclosed in US2005/0195690A1 performs a comparison of the bit sequence with a template of the binary bit sequence indicating the code “P: position marker”, a template of the binary bit sequence indicating the code “1”, and a template of the binary bit sequence indicating the code “0”, respectively, so as to obtain the correlation thereof. Thus, it is judged which of the codes “P”, “1”, and “0” the bit sequence corresponds to based on the correlation.
In the technique disclosed in US2005/0195690A1, the TCO data which is the binary bit sequence is obtained so as to perform the matching with the template. Thus, in a state where the electric intensity is weak or many noises are contained in the demodulated signal, the obtained TCO data is likely to contain a lot of errors. Accordingly, one had to perform fine adjustments to a filter to remove the noises from the demodulated signal and a threshold of the AD converter, so as to improve the quality of the TCO data.
Further, when the data having a unit of time length (1 second) is judged to have any one of the codes “P”, “1”, and “0”, another judgment processing has to be performed for the beginning of a second, and the beginning of a minute, based on the obtained judgment results. Here, when the beginning of the second and the beginning of the minute cannot be detected suitably, the processing is required to be undergone again.
The present invention is made for the purpose of providing: a time information obtaining device in which the beginning position of the codes of the standard time radio wave can be specified and the codes included in the standard time radio wave can be suitably obtained, without being influenced by the state of the electric intensity and the noises of the signals; and a radio clock comprising the time information obtaining device.